Building topography in the Northern Hellenides: insights from geomorphic analysis and cosmogenic nuclides

The Northern Hellenides are located on the eastern margin of the Adria plate, and represent the central segment of the Dinarides-Hellenides orogenic belt. Situated at the junction between continental subduction to the north and oceanic subduction to the south, the Albanian region offers a prime location for studying the interaction between surface and deep geological processes in the Central Mediterranean area. The coexistence of compressive and extensional tectonic styles over short distances strongly contributes to shaping the landscape (Burchfiel et al., 2008), and it is still reflected in the modern focal mechanisms (D’Agostino et al., 2022). Morphological and seismic evidence indicates intense tectonic activity in this region at least since the late Quaternary, a period that is also characterised by intense climatic variability. In this research, we investigate the landscape's response to tectonics and climate by 1) performing an extensive tectonic, geomorphic and fluvial analysis, and 2) calculating basin-wide denudation rates using cosmogenic nuclides.
Basin-wide denudation rates were calculated using cosmogenic Beryllium nuclides across 19 basins distributed throughout various tectonic and geological domains of the orogenic belt. The presence of different lithologies including limestones, ophiolites, silicates, and metamorphic rocks required the use of the in situ 10Be technique for catchments draining quartz-bearing lithologies, and the new meteoric 10Be/9Be technique for areas dominated by quartz-poor lithologies.
Denudation rates exhibit a significant spatial variability ranging from 0.1 mm/yr to over 1 mm/yr, with higher values concentrated in the central part of Albania, where the transition from compressional to extensional domains occurs. The observed spatial variability in denudation rates likely reflects variations in uplift rates. Geomorphological analysis underscores the transient nature of the Albanian orogen, marked by elevated relict surfaces, non-lithological knickpoints, evidence of recent drainage reorganisation and river terraces, reflecting also Quaternary climatic fluctuations. Projections of rivers draining the relict landscape cluster around three ranges of elevation, possibly recording separate episodes of relative base-level changes due to accelerations in rock uplift rates.
We interpret these findings as the result of the interplay between deep crustal accretion, occurring at the regional scale over long periods (>106 years), and the activity of upper crust normal faults at shallower levels since the Pliocene (Guzmán et al., 2013; Pashko et al., 2020). At the local scale, fault activity seems to influence the observed spatial variation of denudation rates. The consistency of denudation rates with incision rates, calculated from river terraces, and with GNSS vertical rates (Serpelloni et al., 2022) further supports our results, offering new insights into the geodynamic evolution of the Northern Hellenides.